Photomask manufacturing method and semiconductor device manufacturing method

ABSTRACT

This invention discloses a photomask manufacturing method. A pattern dimensional map is generated by preparing a photomask in which a mask pattern is formed on a transparent substrate, and measuring a mask in-plane distribution of the pattern dimensions. A transmittance correction coefficient map is generated by dividing a pattern formation region into a plurality of subregions, and determining a transmittance correction coefficient for each of the plurality of subregions. The transmittance correction value of each subregion is calculated on the basis of the pattern dimensional map and the transmittance correction coefficient map. The transmittance of the transparent substrate corresponding to each subregion is changed on the basis of the transmittance correction value.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application is based upon and claims the benefit of priority fromprior Japanese Patent Application No. 2006-202385, filed Jul. 25, 2006,the entire contents of which are incorporated herein by reference.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to a method of manufacturing a photomaskhaving a mask pattern on a transparent substrate and, more particularly,to a method of manufacturing a photomask in which the transmittance of atransparent substrate changes depending on the position. The presentinvention also relates to a semiconductor device manufacturing methodusing a photomask manufactured by this method.

2. Description of the Related Art

Along with the recent advance in the micropatterning of semiconductordevices, a demand for micropatterning in the photolithography process isincreasing. The design rule of leading-edge devices has already reducedthe half pitch (hp) to 45 nm. An exposure technique using both immersionexposure and polarization illumination manages to cope with thismicropatterning.

Under the circumstances, the dimensional uniformity required for aphotomask is increasingly becoming stricter to the degree that thein-plane uniformity of the mask pattern dimensions must be 2 nm (3σ). Tocorrect the mask pattern dimensions, a technique of changing thetransmittance of a quartz substrate is available. This techniquedecreases the transmittance of quartz at a relatively large opening ofthe mask pattern within the mask plane. This allows an exposureapparatus to actually transfer a pattern having substantially desireddimensions onto a wafer. One approach capable of decreasing thetransmittance of the quartz substrate is to form a fine heterogeneouslayer in the substrate using a femto second laser to scatter exposurelight by this heterogeneous layer (e.g., see A2 in PCT [WO]2005/008333).

This approach adjusts the transmittance change amount of the quartzsubstrate while maintaining the relationship with the mask in-planedimensional distribution constant. More specifically, this approachdefines the transmittance change amount as 1% when the dimensions on themask are shifted from a desired value by 1 nm, and maintains thisrelationship between the dimensions on the mask and the transmittanceconstant within the mask plane. That is, this approach decreases by 3%the transmittance of quartz at an opening that is larger than a desiredvalue of the dimensions on the mask by 3 nm.

The relationship between the dimensions on the mask and thetransmittance (to be referred to as the transmittance correctioncoefficient hereinafter) is generally adjusted for a finest patterncalled a cell portion. However, it has begun to be understood that sincenot only fine patterns but also rough patterns are present on the mask,the adjustment of the transmittance correction coefficient for the cellportion results in overcorrection in some regions. This is because afiner pattern suffers a larger dimensional fluctuation on the waferrelative to the dimensional fluctuation on the mask, and therefore has alarger value of a so-called mask error enhancement factor (MEF).

The MEF is given by:

MEF=(mask magnification)×(dimensional fluctuation on wafer)/(dimensionalfluctuation on mask)  (1)

As the current wafer exposure apparatus adopts ¼ reduction transfer, themask magnification is normally 4. When a pattern to be transferred issufficiently larger than the exposure wavelength, the MEF becomesalmost 1. In this case, the dimensional fluctuation on the wafer isequivalent to ¼ that on the mask. This is because the wafer exposureapparatus adopts ¼ reduction transfer.

However, the recent lithography process of forming a micropattern equalto or smaller than the exposure wavelength uses an MEF of 2 or more tobe more sensitive to the dimensional fluctuation on the mask. Forexample, a fine pattern need only undergo transmittance correction by 1%per nm, while a rough pattern need only undergo transmittance correctionby 0.5% per nm. Hence, the adjustment of the transmittance correctioncoefficient for a fine pattern results in overcorrection of a roughpattern.

As described above, the conventional method of changing thetransmittance of a quartz substrate to correct the pattern dimensions ofa mask cannot accurately correct the transmittance because the MEF valuechanges depending on the pattern dimensions.

BRIEF SUMMARY OF THE INVENTION

According to an aspect of the present invention, there is provided aphotomask manufacturing method comprising:

preparing a photomask in which a mask pattern is formed on a transparentsubstrate;

generating a pattern dimensional map by measuring a mask in-planedistribution of pattern dimensions;

generating a transmittance correction coefficient map by dividing aformation region of the pattern into a plurality of subregions anddetermining a transmittance correction coefficient for each subregion inaccordance with a size of a pattern of said each subregion;

calculating a transmittance correction value of said each subregion onthe basis of the pattern dimensional map and the transmittancecorrection coefficient map; and

changing a transmittance of the transparent substrate corresponding tosaid each subregion on the basis of the transmittance correction value.

According to another aspect of the present invention, there is provideda photomask manufacturing method comprising:

preparing a photomask in which a mask pattern formed from a halftonefilm is formed on a transparent substrate;

generating a transmittance correction coefficient map by dividing aformation region of the pattern into a plurality of subregions,calculating, for each subregion, a mask error enhancement factorindicating, when the pattern of the photomask is transferred onto asemiconductor wafer, a relationship between a dimensional fluctuation onthe mask and a dimensional fluctuation on the wafer, selecting andusing, as an MEF value indicating the mask error enhancement factor, amaximum MEF value of a plurality of patterns within each subregion, anddetermining a transmittance correction coefficient of said eachsubregion on the basis of the selected maximum MEF value;

generating a pattern dimensional map indicating a mask in-planedistribution of pattern dimensions by measuring the dimensions of thepattern for each subregion that is larger than the subregions divided indetermining the transmittance correction coefficients;

calculating a transmittance correction value of said each subregion onthe basis of the pattern dimensional map and the transmittancecorrection coefficient map; and

changing a transmittance of the transparent substrate corresponding tosaid each subregion on the basis of the transmittance correction value.

According to still another aspect of the present invention, there isprovided a semiconductor device manufacturing method comprising:

preparing a photomask in which a mask pattern is formed on a transparentsubstrate;

generating a pattern dimensional map by measuring a mask in-planedistribution of pattern dimensions;

generating a transmittance correction coefficient map by dividing aformation region of the pattern into a plurality of subregions anddetermining a transmittance correction coefficient for each subregion inaccordance with a size of a pattern of said each subregion;

calculating a transmittance correction value of said each subregion onthe basis of the pattern dimensional map and the transmittancecorrection coefficient map;

changing a transmittance of the transparent substrate corresponding tosaid each subregion on the basis of the transmittance correction value;and

transferring the pattern of the photomask onto a wafer using thephotomask whose transmittance of the transparent substrate is changed.

BRIEF DESCRIPTION OF THE SEVERAL VIEWS OF THE DRAWING

FIG. 1 is a flowchart showing a photomask manufacturing processaccording to the first embodiment;

FIG. 2 is a view illustrating an example of a transmittance correctioncoefficient map used in the first embodiment;

FIGS. 3A to 3C are views showing a process from photomask formationuntil pattern transfer;

FIG. 4 is a view illustrating an example of a pattern dimensional mapused in the first embodiment;

FIG. 5 is a view illustrating an example of a transmittance correctionvalue map used in the first embodiment; and

FIG. 6 is a flowchart showing a photomask manufacturing processaccording to the second embodiment.

DETAILED DESCRIPTION OF THE INVENTION

Embodiments of the present invention will be described in detail belowwith reference to the accompanying drawing.

First Embodiment

FIG. 1 is a flowchart for explaining a photomask manufacturing methodaccording to the first embodiment of the present invention. FIG. 1 showsa process until a semiconductor device is manufactured after photomaskmanufacture.

First, 80-mm-square pattern data to be formed on a mask was divided into500-μm-square regions (step S1). A transmittance correction coefficientwas determined for each region (step S2). A transmittance correctioncoefficient map as shown in FIG. 2 was generated (step S3). Thetransmittance correction coefficient was determined depending on thepattern size. More specifically, the transmittance correctioncoefficient was calculated using the average pattern pitch within the500-μm-square region. The narrower the pattern pitch, the larger thetransmittance correction coefficient.

Next, as shown in FIG. 3A, an ArF halftone (HT) pattern 32 made ofMoSiON was formed, as a mask pattern, on a quartz substrate 31 servingas a transparent substrate by the normal mask manufacturing process(step S4). The photomask thus manufactured had already undergone defectinspection and defect correction. A scanning electron microscope (SEM)measured the dimensions of the formed HT pattern (step S5). 441 pointswithin the 80-mm-square pattern were measured at a pitch of 4 mm. On thebasis of this measurement data, an 80-mm-square pattern dimensional mapas shown in FIG. 4 was generated (step S6).

This pattern dimensional map describes not the pattern dimension valuesthemselves but the relative values of an actual pattern to a desiredpattern. This is because the principle of transmittance correction candecrease the transmittance but cannot increase it. More specifically,this map uses pattern measurement values at which the HT-omitted patterndimension (i.e., the width of a pattern without any HT) is minimum as areference. That is, this map describes all the values with positivesigns. The larger the value, the larger the HT-omitted patterndimension.

On the basis of the transmittance correction coefficient map shown inFIG. 2 and the pattern dimensional map shown in FIG. 4, a transmittancecorrection value was determined for each 500-μm-square region (step S7).That is, a transmittance correction value was calculated by multiplyingthe transmittance correction coefficient of an arbitrary 500-μm-squareregion divided as the transmittance correction coefficient map by thepattern dimension difference of the pattern dimensional mapcorresponding to this region. A transmittance correction value map asshown in FIG. 5 was thus generated. The value of this correction valuemap indicates the amount of transmittance to be decreased. For example,if the transmittance correction value is 5, the transmittance decreasesby 5%. The measurement points on the pattern dimensional map are spacedapart at a pitch of 4 mm, so this is inconsistent with the region sizeof 500 μm. Therefore, the intervals between the measurement points wereinterpolated by an interpolation method.

As shown in FIG. 3B, a laser beam 33 is guided onto the quartz substrate31 to partially decrease its transmittance (step S8). More specifically,using a laser transmittance correction apparatus (PCT [WO] 2005/008333),a heterogeneous layer having a refractive index different from that ofthe quartz substrate 31 was formed in it by femto second laser beamirradiation to decrease its transmittance. At this time, thetransmittance correction apparatus (CDC) read the transmittancecorrection value map to decrease the transmittance by following thetransmittance correction value map.

Using the normal photomask manufacturing process, the mask underwentcleaning and pellicle adhesion to complete a photomask (step S9). Asshown in FIG. 3C, using this photomask, a pattern was reduced andtransferred onto a resist 36 on a wafer 35 via a projection lens 34(step S10). More specifically, this photomask was set on an immersionexposure apparatus to transfer a device pattern having a half pitch of45 nm onto the resist 36 on the wafer 35. Furthermore, the wafer 35 wasetched using the resist 36 as a mask to manufacture a semiconductordevice (step S11). Consequently, the uniformity of the patterndimensions improved as compared with the prior art. This increased themargin of lithography to be able to greatly improve the semiconductordevice manufacturing yield.

According to the first embodiment, a transmittance correctioncoefficient map is generated for each predetermined region within themask plane, and also a pattern dimensional map within the mask plane isgenerated. The correction value of each transmittance correction regionis calculated on the basis of the transmittance correction coefficientmap and pattern dimensional map. This makes it possible to correct thetransmittance of the quartz substrate with a higher accuracy than in theprior art. It is therefore possible to manufacture a very finesemiconductor device having an hp as narrow as 45 nm or less with a highyield.

Second Embodiment

FIG. 6 is a flowchart for explaining a photomask manufacturing methodaccording to the second embodiment of the present invention. The basicprocess of the second embodiment is the same as that of the firstembodiment. The second embodiment is different from the first embodimentin determining a transmittance correction coefficient on the basis of anMEF value set for each region.

In the second embodiment, as in the first embodiment, first,80-mm-square pattern data to be formed on a mask was divided into500-μm-square regions (step S1). A maximum MEF value within each regionwas determined as its MEF value (step S12). Transmittance correctioncoefficients as shown in FIG. 2 were determined on the basis of theseMEF values (step S2). The relationship between the MEF value and thetransmittance correction coefficient is uniquely determined andgenerally expressed by a linear equation. That is,

(transmittance correction coefficient)=A×(MEF value)+B  (2)

where A and B are preset constants. A transmittance correctioncoefficient map was generated on the basis of the determinedtransmittance correction coefficients of the respective regions (stepS3).

Next, an ArF HT pattern made of MoSiON was formed on a quartz substrateby the normal mask manufacturing process (step S4). This photomask hadalready undergone defect inspection and defect correction. An SEMmeasured the dimensions of the formed HT pattern (step S5). 441 pointswithin the 80-mm-square pattern were measured at a pitch of 4 mm. On thebasis of this measurement data, an 80-mm-square pattern dimensional mapas shown in FIG. 4 was generated (step S6).

On the basis of the transmittance correction coefficient map shown inFIG. 2 and the pattern dimensional map shown in FIG. 4, a transmittancecorrection value was determined for each 500-μm-square region (step S7).Subsequently, as in the first embodiment, the transmittance wasdecreased by following the transmittance correction value map using alaser transmittance correction apparatus (CDC) (step S8).

As in the first embodiment, using the normal photomask manufacturingprocess, the mask underwent cleaning and pellicle adhesion to complete aphotomask (step S9). This photomask was set on an immersion exposureapparatus to transfer a device pattern having a half pitch of 45 nm ontoa resist (step S10). Furthermore, the wafer was etched using the resistas a mask to manufacture a semiconductor device (step S11).Consequently, the uniformity of the pattern dimensions improved ascompared with the prior art. This increased the margin of lithography tobe able to greatly improve the semiconductor device manufacturing yield.

According to the second embodiment, in addition to the first embodiment,the MEF of each predetermined region within the mask plane is calculatedto determine the relationship between the MEF value and thetransmittance correction coefficient in advance. This makes it possibleto correct the transmittance of the quartz substrate with a higheraccuracy than in the first embodiment. It is therefore possible tomanufacture a very fine semiconductor device having an hp as narrow as45 nm or less with a high yield.

Third Embodiment

The third embodiment of the present invention will be explained. Thisembodiment is basically the same as the second embodiment but uses ionimplantation in place of laser beam irradiation to perform transmittancecorrection.

In the third embodiment, first, 80-mm-square pattern data to be formedon a mask was divided into 1-mm-square regions to determine an MEF valuefor each region. The intermediate value between a maximum MEF value andthe average MEF value within each region was determined as its MEFvalue. Transmittance correction coefficients were determined on thebasis of these MEF values. A transmittance correction coefficient map asshown in FIG. 2 was generated on the basis of the transmittancecorrection coefficients of the respective regions, in the same manner asin the second embodiment.

Next, an ArF halftone (HT) pattern made of MoSiON was formed on a quartzsubstrate by the normal mask manufacturing process. This photomask hadalready undergone defect inspection and defect correction. An SEMmeasured the dimensions of the formed HT pattern. 441 points within the80-mm-square pattern were measured at a pitch of 4 mm. On the basis ofthis measurement data, an 80-mm-square pattern dimensional map as shownin FIG. 4 was generated. This pattern dimensional map describes not thepattern dimensional values themselves but relative values.

On the basis of the transmittance correction coefficient map shown inFIG. 2 and the pattern dimensional map shown in FIG. 4, a transmittancecorrection value was determined for each 1-mm-square region. In thethird embodiment, transmittance correction was performed by implantingions into the quartz substrate. The implanted ions are Ga ions. The ionimplantation amount is changed for each 1-mm-square region in the rangeof 2×10¹⁴ to 2×10¹⁶ ions/cm² to decrease the transmittance by followingthe transmittance correction value map. The inventors of the presentinvention experimentally confirmed that implanting Ga ions of about 10¹⁵ions/cm² into the quartz substrate decreased the transmittance by about15%.

Using the normal photomask manufacturing process, the mask underwentcleaning and pellicle adhesion to complete a photomask. This photomaskwas set on an immersion exposure apparatus to transfer a device patternhaving a half pitch of 45 nm onto a resist. Then, it was confirmed thatthe uniformity of the pattern dimensions improved as compared with theprior art. This increased the margin of lithography to be able togreatly improve the semiconductor device manufacturing yield.

According to the third embodiment, it is possible to obtain not only thesame effect as that of the second embodiment but also the followingeffect. That is, using ion implantation for transmittance correctionmakes it possible to set the amount of decrease in transmittance by theion implantation amount with ease and high controllability. This alsomakes it possible to more accurately correct the transmittance of thequartz substrate. The Ga ion does not make the corrected transmittanceof the quartz substrate unstable. That is, even when a wafer exposureapparatus irradiates the mask having undergone transmittance correctionwith an ArF excimer laser beam, the Ga ion can semipermanently maintainthe corrected transmittance at the same level. Furthermore, a change inthe flatness of the mask before and after ion implantation is as smallas 20 nm or less, so a Ga ion is very suitable for transmittancecorrection.

(Modification)

The present invention is not particularly limited to the above-describedembodiments. For example, it is possible to appropriately select theaverage MEF value of a plurality of patterns within each region, amaximum MEF value, or the intermediate MEF value between the average MEFvalue and the maximum MEF value. Alternatively, the MEF value of arepresentative pattern (an important pattern whose dimensions arestrictly managed) within each region may be selected. The inventors ofthe present invention confirmed that the use of a maximum MEF value islikely to result in slight overcorrection, while the use of the averageMEF value is likely to result in slight undercorrection. Hence, the useof the intermediate MEF value between the average MEF value and themaximum MEF value is preferable.

Although the above-described embodiments have exemplified the casewherein a halftone pattern is used as the mask pattern, a pattern formedfrom only a normal light-shielding film may be used. The method ofdecreasing the transmittance of a quartz substrate is also notparticularly limited to a femto second laser or ion implantation as longas energy beam irradiation partially decreases its transmittance. Thetransparent substrate is also not particularly limited to a quartzsubstrate as long as it exhibits a sufficiently high transmittance withrespect to exposure light. The ions implanted into the transparentsubstrate to decrease its transmittance are also not particularlylimited to Ga ions, and can use other ions such as xenon ions.

Additional advantages and modifications will readily occur to thoseskilled in the art. Therefore, the invention in its broader aspects isnot limited to the specific details and representative embodiments shownand described herein. Accordingly, various modifications may be madewithout departing from the spirit or scope of the general inventiveconcept as defined by the appended claims and their equivalents.

1. A photomask manufacturing method comprising: preparing a photomask inwhich a mask pattern is formed on a transparent substrate; generating apattern dimensional map by measuring a mask in-plane distribution ofpattern dimensions; generating a transmittance correction coefficientmap by dividing a formation region of the pattern into a plurality ofsubregions and determining a transmittance correction coefficient foreach subregion in accordance with a size of a pattern of said eachsubregion; calculating a transmittance correction value of said eachsubregion on the basis of the pattern dimensional map and thetransmittance correction coefficient map; and changing a transmittanceof the transparent substrate corresponding to said each subregion on thebasis of the transmittance correction value.
 2. A method according toclaim 1, wherein the mask pattern includes one of a halftone pattern anda light-shielding pattern.
 3. A method according to claim 1, wherein thetransmittance correction coefficient is determined in accordance with anaverage pattern pitch within each of the plurality of dividedsubregions.
 4. A method according to claim 1, wherein to generate thetransmittance correction coefficient map, a mask error enhancementfactor indicating, when the pattern of the photomask is transferred ontoa semiconductor wafer, a relationship between a dimensional fluctuationon the mask and a dimensional fluctuation on the wafer is calculated todetermine the transmittance correction coefficient of said eachsubregion on the basis of the mask error enhancement factor.
 5. A methodaccording to claim 4, wherein one of an average MEF value of a pluralityof patterns within each of the plurality of divided subregions, amaximum MEF value, and an intermediate MEF value between the average MEFvalue and the maximum MEF value is selected and used as an MEF valueindicating the mask error enhancement factor.
 6. A method according toclaim 3, wherein to generate the pattern dimensional map, the dimensionsof the pattern are measured for each subregion that is larger than thesubregions divided in determining the transmittance correctioncoefficients.
 7. A method according to claim 1, wherein to change thetransmittance of the transparent substrate, a heterogeneous region isformed in the transparent substrate by irradiating the transparentsubstrate with a laser beam.
 8. A method according to claim 1, whereinto change the transmittance of the transparent substrate, ions areimplanted into the transparent substrate by an ion implantation method.9. The method according to claim 1, wherein the pattern dimension mapdescribes a relative value of an actual pattern to a desired pattern.10. A photomask manufacturing method comprising: preparing a photomaskin which a mask pattern formed from a halftone film is formed on atransparent substrate; generating a transmittance correction coefficientmap by dividing a formation region of the pattern into a plurality ofsubregions, calculating, for each subregion, a mask error enhancementfactor indicating, when the pattern of the photomask is transferred ontoa semiconductor wafer, a relationship between a dimensional fluctuationon the mask and a dimensional fluctuation on the wafer, selecting andusing, as an MEF value indicating the mask error enhancement factor, amaximum MEF value of a plurality of patterns within each subregion, anddetermining a transmittance correction coefficient of said eachsubregion on the basis of the selected maximum MEF value; generating apattern dimensional map indicating a mask in-plane distribution ofpattern dimensions by measuring the dimensions of the pattern for eachsubregion that is larger than the subregions divided in determining thetransmittance correction coefficients; calculating a transmittancecorrection value of said each subregion on the basis of the patterndimensional map and the transmittance correction coefficient map; andchanging a transmittance of the transparent substrate corresponding tosaid each subregion on the basis of the transmittance correction value.11-19. (canceled)